Project Summary/Abstract Our current ability to detect infants at-risk for neurodevelopmental disorders (NDs) such as autism spectrum disorder (ASD) that cannot be readily identified through screening for biological markers offers several unique opportunities for understanding the emergence of ND symptoms. Particularly important is the opportunity to test the extent to which very early interventions may prevent NDs from emerging or minimize the functional impairments of NDs. Extensive research demonstrates positive associations between parent responsiveness and social-communication outcomes in children with NDs. However, the effects of early interventions designed to improve outcomes for infants/toddlers at risk for or diagnosed with NDs by increasing parent responsiveness have been highly variable. Thus, the available evidence does not provide clear evidence on whether parent responsiveness interventions improve infant/toddler social-communication development, and why or why not. The current project involves a ?proof of concept? evaluation of a newly developed intervention for infants identified as at-risk for NDs through a community screening. This intervention, Parents and Infants Engaged (PIE), is designed to directly impact parent responses to behaviors commonly observed in infants at-risk for NDs that, in the absence of intervention, may not elicit parental responses that promote infants' social- communication development. PIE includes two key content domains: (a) attuning parent responses to infants' behavior reactions to sensory stimuli, including hypo (under)-reactions and hyper (over)-reactions; and (b) attuning parent responses to infants' prelinguistic communicative behaviors, including lower-level behaviors that are not clearly directed to the parent and higher-level behaviors by which infants are clearly intending to communicate with the parent. Study Phase 1 evaluates the separate impact of each domain on infant joint engagement with parents by randomizing 40 infants at-risk for NDs (ages 9 ? 15 months) and a parent of each infant to either the Sensory Reactivity or Prelinguistic Communication domain of PIE. A trained PIE coach will facilitate parents' observations and interpretation of their infants' behaviors relevant to the PIE domain to which each dyad was randomized. The coach also will collaborate with parents to explore different parental responses to infant behaviors, and evaluate whether different parent responses help the infants engage better with the environment and their parents. In Study Phase 2, each dyad will be coached on the PIE component to which they were not exposed in Study Phase 1 (along with continued coaching on the PIE domain addressed in Study Phase 1). Study Phase 2 evaluates the combined effects of the full PIE intervention on parent responsiveness and infant engagement and intentional communication, compared to Pretest and to the effects found for the separate domains of PIE examined in Study Phase 1. The study also examines the impact of PIE on physiological measures associated with infants' ability to regulate their own arousal levels.